Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754589AbZKHQQR (ORCPT ); Sun, 8 Nov 2009 11:16:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753039AbZKHQQQ (ORCPT ); Sun, 8 Nov 2009 11:16:16 -0500 Received: from [95.166.99.235] ([95.166.99.235]:43086 "EHLO kernel.dk" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752601AbZKHQQQ (ORCPT ); Sun, 8 Nov 2009 11:16:16 -0500 Date: Sun, 8 Nov 2009 17:16:21 +0100 From: Jens Axboe To: Corrado Zoccolo Cc: Linux-Kernel , Jeff Moyer Subject: Re: [PATCH] cfq-iosched: fix next_rq computation Message-ID: <20091108161620.GM8742@kernel.dk> References: <200911072237.01807.czoccolo@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200911072237.01807.czoccolo@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2133 Lines: 42 On Sat, Nov 07 2009, Corrado Zoccolo wrote: > Cfq has a bug in computation of next_rq, that affects transition > between multiple sequential request streams in a single queue > (e.g.: two sequential buffered writers of the same priority), > causing the alternation between the two streams for a transient period. > > 8,0 1 18737 0.260400660 5312 D W 141653311 + 256 > 8,0 1 20839 0.273239461 5400 D W 141653567 + 256 > 8,0 1 20841 0.276343885 5394 D W 142803919 + 256 > 8,0 1 20843 0.279490878 5394 D W 141668927 + 256 > 8,0 1 20845 0.292459993 5400 D W 142804175 + 256 > 8,0 1 20847 0.295537247 5400 D W 141668671 + 256 > 8,0 1 20849 0.298656337 5400 D W 142804431 + 256 > 8,0 1 20851 0.311481148 5394 D W 141668415 + 256 > 8,0 1 20853 0.314421305 5394 D W 142804687 + 256 > 8,0 1 20855 0.318960112 5400 D W 142804943 + 256 > > The fix makes sure that the next_rq is computed from the last > dispatched request, and not affected by merging. > > 8,0 1 37776 4.305161306 0 D W 141738087 + 256 > 8,0 1 37778 4.308298091 0 D W 141738343 + 256 > 8,0 1 37780 4.312885190 0 D W 141738599 + 256 > 8,0 1 37782 4.315933291 0 D W 141738855 + 256 > 8,0 1 37784 4.319064459 0 D W 141739111 + 256 > 8,0 1 37786 4.331918431 5672 D W 142803007 + 256 > 8,0 1 37788 4.334930332 5672 D W 142803263 + 256 > 8,0 1 37790 4.337902723 5672 D W 142803519 + 256 > 8,0 1 37792 4.342359774 5672 D W 142803775 + 256 > 8,0 1 37794 4.345318286 0 D W 142804031 + 256 Thanks, this is a nice patch! I will apply it to for-2.6.33. Can I added your signed-off-by? -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/